The purpose of this research is to determine the occupational risks among workers in an atomic energy facility. A major objective is to study the long-term delayed biological effects of low-level ionizing radiation in a normal adult industrial population, who have been chronically exposed to fractionated doses of low-level ionizing radiation over a span of years. The study is a prospective epidemiological evaluation of workers employed since 1944 and in succeeding years to be followed for cause of death identification through 1979, in which known radiation measurements have been made and recorded on a uniform basis during the entire period of employment. The National Social Security System is utilized for the identification of the deceased and the state vital records provide the cause of death data. A control population for the Hanford employees matched to the 35,000 atomic worker population has been established and will be processed simultaneously through Social Security with the employees for the identification of mortality data. Previous analyses have been confined to Hanford employees, 1976. Successive cohort analyses of employee populations, with simultaneous control of employment exposures, employment patterns, occupations, and external and internal radiation measurements will be carried out.